TP: fixes bug that surfaces when trying to compare profiles without params

[mitchell852]

What does this PR (Pull Request) do?

This PR fixes a bug highlighted by a failing UI test. When comparing 2 profiles, if one or both of the profiles has no params, then the comparison page fails to load.

• This PR is not related to any Issue

• No tests as this is a scenario covered by a current UI test

• No documentation as this is simply a bug fix

• No changelog.md entry as this bug was not released with any TC release

Which Traffic Control components are affected by this PR?

• Traffic Portal

What is the best way to verify this PR?

• In TP, navigate to the profiles view - tp.domain.com/#!/profiles
• Select 2 profiles to compare. Ensure that at least one of those profiles has ZERO params associated with it
• Ensure that the profile diff page is displayed correctly.

If this is a bug fix, what versions of Traffic Control are affected?

• master (0974c74)

The following criteria are ALL met by this PR

• This PR includes tests OR I have explained why tests are unnecessary
• This PR includes documentation OR I have explained why documentation is unnecessary
• This PR includes an update to CHANGELOG.md OR such an update is not necessary
• This PR includes any and all required license headers
• This PR ensures that database migration sequence is correct OR this PR does not include a database migration
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)

Additional Information

[asf-ci]

Refer to this link for build results (access rights to CI server needed):
https://builds.apache.org/job/trafficcontrol-PR/4600/

[ocket8888]

Works, tests pass, no _.js.